Part 1: Simulating Mitosis Investigation 7 Report REVIEW MATERIALS AND SUMMARY CELL DIVISION: MITOSIS AND MEIOSIS Think about these questions as you review the cell cycle and mitosis. If a cell contains a set of duplicated chromosomes, does it contain any more genetic information than the cell before the chromosomes were duplicated? What is the significance of the fact that chromosomes condense before they are moved? How are the chromosome copies, called sister chromatids, separated from each other? What would happen if the sister chromatids failed to separate?
Part 2: Effects of Environment on Mitosis This exercise is supported by the premise that lectins increase the rate of mitosis in the roots. Lectins are proteins that bind to specific carbohydrate groups. Notes about the lectin: Phytohemagglutinin (PHA-M) is a lectin; a lectin is a protein that binds to specific carbohydrates. PHA-M induces mitosis (acts as a mitogen) in cultured T-lymphocytes by binding to the T-cell receptor for antigen (part of the Ti-C3 complex). This causes an intracellular signal involving Ca2+ release from the endoplasmic reticulum, ultimately causing cell replication. Alternative Procedure The root tips on prepared slides are segmented with masking tape for the three root regions: Region of Cell Division, Region of Elongation, Region of Maturation. You will count the number of cells in interphase and mitosis for specified regions. Table 1. Onion Root Tip Cell Phase Data; Treatment Group Number of Cells Tip Interphase Mitotic Total 1 Region of Cell Division 2 Region of Maturation 3 Region of Elongation Total Table 2. Class Data; Onion Root Tip Cell Phase Data Control (R-Elongation) Treated (R-Cell Div) Class- Number of Cells Interphase (# & %) Mitotic (# & %) Total (# & %) Calculation of Chi-Square for the Region of Cell Division Cells 1. Enter the number of treated cells (R-Cell Div.) in interphase and mitosis as observed (o). 2. Calculate the percentage of cells in interphase and mitosis in the control group from Table 2. 3. Multiply the percentages by the total number of cells in the treated group; this will give the expected numbers (e). 4. Calculate the chi-square (χ2) value for the test. 5. Compare this value to the critical value in Table 5.
Table 3. Calculation of Chi-Square Region of Cell Division Cells χ2 =Σ (o-e)2/e = Interphase Cells Mitosis Cells # Observed (o) # Expected (e) (o-e) (o-e)2 (o-e)2/e Table 4. Calculation of Chi-Square Region of Elongation Cells χ2 =Σ (o-e)2/e = Interphase Cells Mitosis Cells # Observed (o) # Expected (e) (o-e) (o-e)2 (o-e)2/e Table 5. Critical Values of the Chi-Square Distribution Probability Degrees of Freedom (df) 1 2 3 4 5 0.05 3.84 5.99 7.82 9.49 11.1 0.01 6.64 9.21 11.3 13.2 15.1 0.001 10.8 13.8 16.3 18.5 20.5 1. The degrees of freedom (df) equals the number of groups minus one. In this case, there are two groups, interphase and mitosis; therefore, df = 2-1 or 1. 2. The p value is 0.05, and the critical value is 3.84. If the calculated chi-square value is greater than or equal to this critical value, then the null hypothesis is rejected. If the calculated chi-square value is less than this critical value, the null hypothesis is not rejected. Postlab Review What was the importance of collecting the class data? Given that plants have a limited amount of energy for cellular processes, describe how energy resources for cellular processes are shifted from one region to the other, beginning with the tip working upward along the root tissue.
Given that the fungal pathogen increases lectin in the root cells, thus stimulating mitosis, develop a hypothesis to explain/test how that results in weakening the plant and causing lower production? Does an increased number of cells in mitosis mean that these cells are dividing faster than the cells in the roots with a lower number of cells in mitosis? Explain. Part 3: Loss of Cell Cycle Control in Cancer. Develop a hypothesis as to how the chromosomes of a normal cell might appear in comparison to a cancer cell. If.then. How might cancer cells be different from normal, healthy cells? How is cellular division fundamentally different from that in normal cells? How are normal cells and cancer cells different from each other? What are the main causes of cancer?
How is the cell cycle controlled in normal cells? What are cyclins and cyclin-dependent kinases? What do these proteins do in a cell? What goes wrong during the cell cycle in cancer cells? What makes some genes related to increased cancer risk? Do you think that the chromosomes might be different between normal and cancer cells? What happens in a normal cell if the DNA has mutations? What would happen if cells with mutated DNA replicate? How do cells monitor DNA integrity? How does infection with human papillomavirus virus increase the risk of cervical cancer?
Part 4: Meiosis Analysis 1. In a two-three sentence response, describe three major differences between the events of mitosis and meiosis and the biological consequences of those differences. a. b. c. 2. How does crossing over contribute to genetic variability? What is the behavioral significance of generating genetic variability in this way from common ancestors? (Hint: research kin selection ).
Part 5: Data for Meiosis and crossing-over in Sordaria 1. As you classify asci, record the sequence of spores within each ascus on the tally sheet a. Each GROUP should classify at least 50 asci to insure an adequate sample size for the class data. Parental asci will have 4 black and 4 tan spores in a row (4:4 pattern). Example: Meiosis with Crossing Over 2:4:2 Arrangement (ttbb, bbtt) 2. Add your count to the class data sheet. Class Data
Part 5 Analysis of Crossing Over Rates in Sordaria Calculations: Ratio of bbtt/:ttbb (Total) 1. Is this distance accurate? If not what other factor needs to be considered? 2. Published results indicate that the map distance from the centromere of the gene for spore color in S. fimicola is 26 map units (corresponds to 52% crossover frequency) Percent crossover asci = bttb + tbbt + tbtb + btbt Total Interstrain Asci X 100 = Map Distance between Centromere and Locus of Tan Gene = % Crossover 2 = 3. How close are your results to the published results?